That's great for you, but as a societal discussion, that's about as useful as a story of how someone prayed and their mom's cancer went away.
You're taking a risk, in the context of a committed relationship where you've already had kids (so the stakes are lower than for a lot of people). So far that risk has worked out for you. That doesn't mean that is the right risk for everyone. It also doesn't mean that what you're doing is reliable for everyone. And it certainly doesn't mean that you're somehow more intelligent or competent than the people for whom similar methods of family planning have failed.
You're taking a risk, in the context of a committed relationship where you've already had kids (so the stakes are lower than for a lot of people). So far that risk has worked out for you. That doesn't mean that is the right risk for everyone. It also doesn't mean that what you're doing is reliable for everyone. And it certainly doesn't mean that you're somehow more intelligent or competent than the people for whom similar methods of family planning have failed.